Islamic State’s willing executioners

We knew it was coming, because the masked killer in the David Haines beheading video, released three weeks ago by Islamic State, warned us that it would be. But it is still profoundly shocking. We know the purported rationale. “We take this opportunity to warn those governments that enter this evil alliance of America against the Islamic State to back off and leave our people alone,” declares the killer in the Steven Sotloff video. But a rationale doesn’t kill. A human being does, often in concert with other human beings.